The invention relates to a method for manufacturing a microelectronic circuit. Furthermore, the invention relates to a corresponding microelectronic circuit.
In the conventional technology, hafnium dioxide (HfO2 or also hafnium(IV) oxide or also hafnia) is often used as a dielectric for microelectronic circuits. For example, it is used as a gate insulator in MISFETs (metal-insulator-semiconductor field effect transistors) or as a dielectric layer of a DRAM memory capacitor. As such, the material is CMOS-compatible, i.e., it may be used with the conventional semiconductor processes for realizing integrated digital or analog circuits. Furthermore, its thickness is scalable and it comprises a high k value. The latter means that it comprises a higher relative permittivity than conventional silicon dioxide. It also comprises a large band gap.
The discovery of ferroelectricity in materials containing hafnium dioxide (in this case with the designation FE-HfO2) (e.g., see T. S. Böschke, J. Müller, D. Bräuhaus, U. Schröder, U. Böttger, “Ferreoelectricity in hafnium oxide thin films”, Applied Physics Letters 99, 102903, 2011) has extended the application to the field of ferroelectric memories (with respect to FRAM, see J. Müller, P. Polakowski, S. Mueller, T. Mikolajick, “Ferreoelectric Hafnium Oxide Based Materials and Devices: Assessment of Current Status and Future Prospects”, ECS Journal of Solid State Science and Technology, 4 (5), N30-N35, 2015).
In particular, ferroelectric field effect transistors (FeFETs) relying on a shift of the threshold voltage of the FET by switching electric dipoles in the gate dielectric are very suitable elements since hafnium dioxide is an established gate oxide material (e.g., see US 2013/0270619 A1 or DE 10 2014 212 483 A1). For example, capacitors with ferroelectric layers are described in US 2007/0045689 A1 or US 2009/0061538 A1. Ferroelectricity refers to the phenomenon that certain materials with an electrical dipole moment may change the direction of spontaneous polarization by applying an external electric field.
In order to realize memories that are separate or embedded into integrated circuits by means of hafnium dioxide FeFETs, further functional components and, in particular, transistors are necessitated, e.g., as input/output points, as amplifiers or multiplexers, so that applying ferroelectric and non-ferroelectric transistors on a common substrate becomes necessitated. Therefore, corresponding microelectronic circuits comprise very different components, each comprising different structures and manufacturing requirements.
For example, the following steps are performed in the conventional technology after producing a shallow trench isolation (STI) for producing different transistors:    1. The silicon surface is prepared for the ferroelectric transistors.    2. The ferroelectric hafnium dioxide is applied onto the entire substrate.    3. In the areas where standard transistors are to be produced, i.e., in this case transistors without ferroelectric hafnium dioxide, the ferroelectric hafnium dioxide is selectively removed—e.g., by using titanium nitride as a mask.    4. The silicon surface is prepared for the standard transistors.    5. The material for the standard transistors, e.g., non-ferroelectric hafnium dioxide, is applied onto the entire wafer.
This is followed by the conventional CMOS steps in order to produce the structures.
It is disadvantageous that the ferroelectric hafnium dioxide is also subjected to the treatment steps for the other components in step 4. The preparation steps are absolutely necessitated in order to obtain logic transistors comprising sufficient reliability and switching speed. In this case, a nitridation (also used in the conventional technology is the term “nitriding”) is performed, e.g., in the form of “rapid thermal nitridation” or plasma nitriding. However, this has a disadvantageous effect on the ferroelectric hafnium dioxide.
Here, logic transistors are generally to be understood as standard transistors serving for realizing a corresponding circuit logic, e.g., for driving transistors with ferroelectric hafnium dioxide. Therefore, both expressions are equivalent to each other. A further problem arises from the polycrystalline structure of the ferroelectric hafnium dioxide and the resulting inhomogeneously distributed surface polarization. In order to control the channel region of a ferroelectric field effect transistor in a stable manner, a homogeneous distribution of the ferroelectric polarization would be desirable.
The disadvantages described do not only relate to hafnium dioxide as a ferroelectric but also to any other material used as a ferroelectric for a ferroelectric capacitor.
The object of the invention is to propose an effective method for manufacturing a microelectronic circuit as well as a corresponding microelectronic circuit. A further object is to propose a method providing increased protection during manufacturing, in particular, for the components comprising sensitive materials.